The disclosed subject matter pertains to linear capacitive image sensors and the methods by which they are operated. Examples of such sensors are described, for example, in U.S. Pat. No. 7,099,496 B2 for Swiped Aperture Capacitive Fingerprint Sensing Systems and Methods issued Aug. 29, 2006, and related successor and subsequent patents, such as U.S. Pat. No. 7,460,697 B2 for Electronic Fingerprint Sensor with Differential Noise Cancellation issued Dec. 2, 2008. In U.S. Pat. No. 7,099,496, a fingerprint sensor is described which includes an image sensor, a rate sensor and a sensing circuit. The described image sensor in U.S. Pat. No. 7,099,496 is an example of a linear array capacitance sensor which is of the type referred in this disclosure. In U.S. Pat. No. 7,460,697 there is disclosed such a sensor with two pickup plates and a differential amplifier to reduce noise effects. U.S. Pat. App. Pub. No. 2009/0252386 A1 for Apparatus and Method for Reducing Parasitic Capacitive Coupling and Noise in Fingerprint Sensing Circuits issued Oct. 8, 2009, discloses such a system where an energized drive plate and adjacent un-energized drive plates are selectively grounded to the same relatively noisy ground, while all other un-energized drive plates are grounded to a separate quiet ground. Aspects of embodiments of the disclosed subject matter in the present application improve upon the noise reduction and signal acquisition features of such devices. In addition aspects of the disclosed subject matter may be implemented in a 2D array of capacitive sensors.
In addition in the field of the disclosed subject matter according to aspects of embodiments of the disclosed subject matter improvement is provided for the needed ability to sense effectively biometric images, such as fingerprint images, through dielectric layers, such as layers of flex material, protective coatings, and layers of glass, such as in displays, etc., the material(s) being of ever increasing total thickness between actual sensor elements and the biometric being sensed, such as a fingerprint on a human finger. Part of the problem is improving the signal level and particularly the signal to noose ratio. Aspects of the disclosed subject matter address these concerns.